Implantation pin, fixation device and method for implanting the implantation pin

ABSTRACT

An implantation pin for implantation in a target structure has a pinhead and a shaft. The pinhead comprises a pinhead moulding portion comprising a moldable material which can be liquefied by application of mechanical energy such as ultrasonic vibration energy. A channel extends through the pinhead and the shaft, the channel connecting the pinhead molding portion to a discharge opening located at the shaft. The moldable material can be liquefied by applying mechanical energy in the form of ultrasonic vibrations via a fixation device including an ultrasonic sonotrode and a vibrating tip. The pressure applied by the vibrating tip can be transmitted via the border of the pinhead to the target structure while the liquefied mouldable material can be forced through the channel and the discharge opening into a gap between the implantation pin and a recess in a target structure thereby fixing the implantation pin in the target structure.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 11/788,761, filed on Apr. 20, 2007, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to an implantation pin, a fixation device, animplantation kit and a method for applying an implantation pin to atarget structure. In particular, the invention relates to a bone pinwhich is formed as a sonic pin.

In the prior art several implantation devices for humans or animals areknown. The implants at least partly create positive-fit connections tohuman or animal tissue parts, particularly skeletal parts, wherein theimplants help connect tissue parts together, or help connect tissueparts to means supporting or replacing tissue parts, or to othertherapeutic auxiliary devices. Further methods for implanting implantsinto humans or animals are known.

Known implants for creating connections to skeletal parts such as bonesinclude screws, pins, staples, etc., which are used for connecting bonesto bones, or bones to artificial, carrying, stabilizing, or supportingparts, or to parts replacing skeletal parts (stabilization or fixationplates, sutures, wires, artificial joint elements, artificial teeth,bone grafts, etc.). Such connection elements for implantation consistfor example of metal or plastic, including resorbable plastic. Afterhealing, the connection elements may be removed by a further operationor they may be left in the body where they are possibly graduallydecomposed and replaced by vital tissue.

For stabilizing a bone fracture, a fixation plate with suitable holesmay be fixed in the region of the fracture using screws as mentionedabove. Plate and screws may consist of metal (e.g. stainless steel ortitanium). The screws may be self-cutting and are rotated intothreadless openings in the bone, or they may be screwed into pre-drilledthreaded openings. Pins may be pushed into previously created openingsfor similar purposes. Connections created in the foregoing manner areusually based on frictional engagement, possibly on positive fit.Substantial pressure may be applied to living tissue during theimplantation.

It is known also to use curable, plastic materials (e.g. particularcements on a water or polymer base) for creating connections of thementioned type. Such materials are pressed from the outside betweenimplant and vital tissue, or into tissue defects in a highly viscouscondition, and are cured in situ. Positive-fit connections can becreated using such material, if the openings into which the material ispressed comprise suitable undercuts. In order to reduce the stressand/or costs of the corresponding operation method so-calledbiodegradable implants, e.g. bone pins, may be used. That is, bone pinswhich degrade over time and which are then absorbed by the body. One ofsuch known biodegradable bone pins is known under the trademark Polypin.This bone pin consists of a polyactid-copolymer mixture and is absorbedduring a period of about two years.

Also known in the art is the usage of thermoplastic polymer materialswhich can be liquefied in a targeted manner by way of mechanicaloscillation such as ultrasonic oscillations and, in this condition, canbe pressed into cavities by way of hydrostatic pressure, therebycreating positive fit connections after solidification.

Such implants may serve for creating positive-fit connections to tissueparts and may consist at least partly of a material that can beliquefied at a relatively low temperature (<250° C.) by way ofmechanical oscillation energy such that the material can be pressed intopores or other openings of the tissue part by the effect of externalpressure to form positive-fit connections when re-solidified.

In a prior art approach an implantation pin for implantation in a targetstructure comprises a base region and a shaft region. The base regioncomprises a connection portion which is adapted to interact with acoupling region of a sonotrode applying ultrasonic vibrations. The shaftregion comprises a material which can be liquefied by applyingultrasonic vibrations. Accordingly, when ultrasonic vibrations aregenerated within the sonotrode and transmitted to the base region of theimplantation pin, these ultrasonic vibrations are further transmitted tothe shaft region. At a surface, where the shaft region abuts to thetarget structure, such as for example a bone into which a recess hasbeen formed in order to accommodate the implantation pin, the localsurface temperature increases due to friction between the targetstructure and the vibrated implantation pin. This surface temperatureincrease causes a melting of the liquefiable material such that thelatter can then flow into pores of the bone. After re-solidifying of theliquefiable material a positive-fit connection between the implantationpin and the bone may be created.

However, with this prior art implantation pin, the surfaces of the shaftregion of the implantation pin which are to be connected to the targetstructure have to be in direct contact to the target structure whileapplying the ultrasonic vibrations. For example, when the implantationpin is to be fixed within a bone, it has to be inserted into apreviously prepared recess within the bone and has to contact the insidesurface walls of the recess in order to liquefy the shaft regionmaterial at these locations. For this purpose, it might be necessary toprecisely adapt the geometry of the implantation pin to the geometry ofthe recess in the bone. Furthermore, it might be necessary to exertsubstantial pressure to the implantation pin while applying theultrasonic vibrations in order to liquefy the shaft region material andthis substantial pressure might be transmitted to the inside surface ofthe recess at which location the bone might be sensible for damages.

Furthermore, the above prior art implantation pin must have sufficientrigidity in order to transmit the ultrasonic vibrations applied to thebase region to the shaft region such that the shaft region issufficiently vibrated in order to melt the liquefiable material at thisshaft location.

Ultrasonic bone implants are disclosed in U.S. Pat. No. 6,921,264 andU.S. Publication No. 2006/0105295 the disclosures of which areincorporated herein by reference.

BRIEF SUMMARY OF THE INVENTION

There may be a need to provide an implantation pin, a fixation device,an implantation kit and a method for applying an implantation pin to atarget structure which may overcome the above described deficiencies ofthe prior art at least in part. Particularly, there may be a need toprovide an implantation pin which is adapted such that liquefiedmoldable material can be provided to an inside of a target structurewithout applying excessive mechanical stress to the target structure'sinside.

This need may be met by an implantation pin, a fixation device, animplantation kit and an implantation method according to the independentclaims. Embodiments of the invention are described in the dependentclaims.

According to a first aspect of the present invention, an implantationpin for implantation in a target structure is provided wherein theimplantation pin comprises a pinhead and a shaft. The pinhead comprisesa pinhead moulding portion comprising a moldable material which can beliquefied by application of energy, preferably mechanical energy. In theimplantation pin a channel extends along the pinhead and the shaft, thechannel connecting the pinhead molding portion to a discharge openinglocated at the shaft.

The implantation pin according to the invention can be used forimplantation in any desired target structure. However, the implantationpin may be specially adapted as a bone pin to be introduced and fixed inbones of humans or animals. For the purpose of implantation, a recess orhole may be prepared in the bone. The recess or hole has a certaingeometry with a given cross-section and depth. The implantation pin maythen be selected such that its shaft has a corresponding geometry with aslightly smaller cross-section and depth. Accordingly, the implantationpin can be inserted with its shaft into the recess or hole but does notneed to have a tight press-fit within the hole.

It may be seen as an aspect of the present invention that the pinhead ofthe implantation pin is adapted such that, when the implantation pin isinserted in the recess or hole within the target structure, a lowersurface of the pinhead being directed substantially in the direction ofthe shaft may abut on the surface of the target structure surroundingthe recess or hole. In such arrangement, an energy source such as anultrasonic vibration source e.g. in the form of an ultrasonic sonotrodemay be applied to the pinhead molding portion such that the moldablematerial comprised therein may be liquefied by application of mechanicalenergy in the form of ultrasonic vibrations. The liquefied moldablematerial can then flow through the channel extending through the pinheadand the shaft to the opposite discharge opening of this channel which islocated at a surface of the shaft, the shaft itself being located withinthe recess or hole. At this location, the liquefied moldable materialcan fill a remaining gap between the shaft of the implantation pin andthe surrounding target structure thereby allowing an advantageouspositive fit of the implantation pin in the target structure afterre-solidification of the moldable material.

For liquefying the moldable material in the pinhead, the ultrasonicvibration source has to be pressed onto the pinhead in order toefficiently transmit the ultrasonic vibration energy into the pinheadmolding portion. However, this pressure is mainly not applied to thepossibly sensitive inside surface of the recess or hole within the boneas the shaft does not need to be press-fitted into this recess or hole.Instead, the pressure may be mainly applied to the outer surface of thebone surrounding the recess or hole which is not as sensitive as it hasnot been damaged previously.

In the following, further features, embodiments and advantages of thepresent invention are presented.

The pinhead may have any desired geometry and may be adapted tocooperate with a source of mechanical energy such as a source ofultrasonic vibrations. The geometry of the shaft should be adapted tothe geometry of the recess in the target structure in which theimplantation pin shall be implanted. As the recess is usually preparedby drilling, the shaft may have an elongated geometry with a circularcross-section. As the recess being prepared by a drilling tool may havea conical end portion, the extremity of the shaft distal to the pinheadmay also have a corresponding conical shape e.g. in the form of apointed tip. However, as, in contrast to the prior art implantationpins, the distal extremity of the shaft is not used to apply a highpressure onto the bone while inserting and fixing the implantation pinwithin the bone, the implantation pin according to the invention doesnot necessarily need such pointed tip but can also be blunt or flat.

The pinhead molding portion can be a partial portion of the pinheadconsisting of a moldable material. Alternatively, the entire pinhead maybe made from a moldable material wherein only a partial region of thepinhead will actually be liquefied as the contact surface between thesource of mechanical energy and the pinhead is only a part surface ofthe entire pinhead.

The moldable material can be any material which can be liquefied byapplication of energy, particularly mechanical energy and moreparticularly by application of ultrasonic vibration energy. In otherwords, the moldable material should be such that it is originally solidand becomes liquid or plasticized upon application of energy.Preferably, the moldable material may be adapted in such a way that itsliquefaction may be achievable by an energy input which does not destroyor harm human tissue, particularly bone tissue. The moldable materialcan be for example a thermoplastic material. Such material can liquefyor plasticize at elevated temperatures. For example, the material andthe geometry of the implantation pin may be chosen such as to exhibit asufficient degree of liquefaction at temperatures below a predeterminedtemperature threshold such as not to substantially harm any tissue.Examples of moldable materials may be thermoplastics such as e.g. PA(Polyamide), PC (Polycarbonate), PP (Polypropylene), PE (Polyethylene),PMMA (Polymethylmethacrylate), POM (Polyoxymethylene), PES(Polyethersulfone), PEI (Polyetherimide), PPSU (Polyphenylsulphone),PEEK (Polyetheretherketone), PSU (Polysulfone) or the bio-compatible orbio-resorbable materials mentioned further below.

The liquefaction of the moldable material should be such that theliquefied material can easily flow through the channel extending fromthe pinhead molding portion. Accordingly, the liquefied material shouldhave such low viscosity that it can be pushed through the channelwithout applying excessive pressure onto the implantation pin in ordernot to damage or harm the target bone structure.

One main characteristic feature of the implantation pin according to theinvention may be seen in the channel connecting the pinhead moldingportion to a discharge opening located spaced apart from this mouldingportion. This channel allows a spatial separation between the locationof applying the mechanical energy thereby liquefying the moldablematerial and the location of applying the liquefied material in a regionbetween the implantation pin's shaft and the surrounding targetstructure. Furthermore, the region where the pressure applied from amechanical energy source is transmitted onto the target structure suchas the bone and the region where the liquefied material is applied tothe target structure via the channel can be different.

It is to be noted that a single channel connecting the pinhead moldingportion to a single discharge opening at the shaft may be sufficient.However, a plurality of channels and/or a channel branching into pluralbranches and leading to a plurality of discharge openings located atdifferent positions at the shaft and/or at the pinhead may be providedin order to distribute the liquefied moldable material in anadvantageous manner to a plurality of locations within the recess in thetarget structure in which the implantation pin is to be located.

According to a further embodiment of the present invention the channelextends internally through the pinhead and the shaft. In other words,the channel has its origin adjacent to the pinhead molding portion andthen runs down through the shaft to the discharge opening. For example,the channel can extend along a middle longitudinal axis of theimplantation pin.

According to a further embodiment of the present invention the at leastone discharge opening of the channel is positioned at a lateral surfaceof the shaft. In this way, the liquefied moldable material can betransferred to the circumferential surface of the shaft such that apositive fit between the lateral surface of the shaft and the side wallsof the recess in the target structure can be obtained.

According to a further embodiment of the present invention the dischargeopening is located at an extremity of the shaft distal from the pinhead.In other words, at least one discharge opening of the channel maydischarge into the recess in the target structure at a position closerto a distal end of the shaft than to the pinhead. Preferably, thedischarge opening is located in a direct proximity to the distal end ofthe shaft. Thereby, liquefied moldable material can exit the channel ata position deep inside the recess within the target structure therebysupporting a secure fixation of the shaft within this recess.

According to a further embodiment the shaft comprises a shaft moldingportion adjacent to the channel, the shaft molding portion comprisingmoldable material which can be liquefied by application of mechanicalenergy. In other words, the implantation pin comprises both a pinheadmolding portion and a shaft molding portion where the material can beliquefied by application of e.g. ultrasonic vibration energy.Accordingly, the molding portions are not only limited to the pinheadbut also extend into the shaft thereby providing a larger volume ofmoldable material. Preferably, the shaft molding portion is locateddirectly adjacent or continuous to the pinhead molding portion.Furthermore, the moldable materials of the pinhead molding portion andthe shaft molding portion may be same or similar.

According to a further embodiment the implantation pin consists entirelyof one single material. In this embodiment, the entire implantation pincan be made from a moldable material and can be fabricated for exampleas a single integral component. In this embodiment, the pinhead moldingportion and/or the shaft molding portion may be defined as partial areasof the implantation pin which, in use, are actually liquefied byapplication of mechanical energy e.g. by using an ultrasonic sonotrodethe geometry of which is specially adapted to the geometry of theimplantation pin. Providing the entire implantation pin with only onematerial may significantly simplify the fabrication of such pin. Forexample, the pin may be made by injection molding.

According to a further embodiment of the present invention the pinheadhas a larger lateral dimension perpendicular to a longitudinal axis ofthe pin than the shaft. In other words, with respect to a widthperpendicular to the longitudinal axis of the pin the pinhead is widerthan the shaft. In this embodiment, if both the pinhead and the shafthave a circular cross-section, the radius of the pinhead is larger thanthe radius of the shaft. Accordingly, the pin can be introduced with itsshaft into a recess in the target structure until the wider pinheadabuts to the circumferential border of the recess. The shaft itself maynot or may only slightly contact the surfaces of the recess in thetarget structure. Thereby, when pressure and vibrations are applied tothe implantation pin, forces are mainly transmitted to the outer surfaceof the target structure such as a bone whereas the inner part of thebone within the recess accommodating the shaft will not or only slightlybe loaded.

According to a further embodiment the channel discharges into aplurality of discharge openings at various surface portions, preferablyat opposing lateral surface portions, of the shaft. In other words thechannel coming from the molding portion may branch off in severalsub-channels which may lead to a plurality of discharge openings. Thesedischarge openings may be positioned at the lateral surface of the shaftat opposing locations such that the liquefied moldable material comingfrom the molding portion can be distributed homogeneously around thelateral surfaces of the shaft. The sub-channel(s) may branch off fromthe middle main-channel in an obtuse angle in order to improve flowingproperties of liquefied moldable material through the channels.

According to a further embodiment, an additional channel extends throughthe pinhead the channel connecting the pinhead molding portion to adischarge opening located at a surface portion of the pinhead. In otherwords, one or more additional channels can be provided within theimplantation pin such that the pinhead molding portion is not onlyconnected to one or more discharge openings at the shaft but also to oneor more additional discharge openings located at the pinhead at asurface which, in use, is directed to or close to the target structureinto which the implantation pin is to be implanted. Thereby, additionalstability of the connection between the implantation pin and the targetstructure can be obtained as the implantation pin is not only “glued” tothe inside of a recess in the target structure but also the pinhead ofthe implantation pin is “glued” to the surface of the target structure.

According to a further embodiment, at least one of a surface coating ofthe implantation pin, a bulk material of the implantation pin and themoldable material comprises a bio-compatible material. A bio-compatiblematerial may be a material which does not negatively interfere withhuman or animal tissue. Examples of bio-compatible materials may bespecially adapted metal alloys such as titanium or specific plastics,e.g. PEEK (Polyetheretherketone), UHMWPE (Ultra high molecular weightpolyethylene), PLA (Polylactic acid), PLLA (Poly-L-lactide), PLDLA(Poly(D,L-Lactide)), PDLLA (Poly-DL-lactide), PVDF (PolyvinylideneDifluoride). Such bio-compatible materials may be used especially forthe outer “skin” of the implantation pin in order to avoid rejection ofthe implantation pin when implanting the pin for example into a bone. Itis advantageous to use a bio-compatible thermoplastics which can be usedboth for the outer skin of the pin as well as for the inner moldablematerial such that the entire implantation pin can be made of thissingle bio-compatible material.

According to a further embodiment at least one of a surface coating ofthe implantation pin, a bulk material of the implantation pin and themoldable material comprises a bio-absorbable material. Suchbio-absorbable material may be absorbed by a human or animal's bodyafter a certain period such that parts of the pin consisting of suchbio-absorbable material may be replaced by living tissue after thisperiod, thereby providing an increased stability of the connectionbetween implantation pin and living tissue and reducing rejectionreactions.

One possible bio-absorbable material comprises a copolymer comprisingbetween 50% and 90% Poly-L-lactide and between 10% and 50% Poly-D,L-lactide. In particular, the bio-absorbable material may be a copolymercomprising 70 weight % Poly-L-lactide and 30 weight % Poly-D, L-lactide.Preferably, the bio-absorbable material may be formed as an amorphousmaterial.

The above described material may be a suitable material for animplantation pin, which material may exhibit a suitable tensile strengthof about 60 MPa, and a suitable E-modulus of about 3500 MPa.Furthermore, an implantation pin including the above material, mayretain its strength for about a sufficient time when implanted into ahuman or animal's body, such a time span may be about 16 to 26 weeks.The described copolymer may have a resorption time of about two to threeyears in a human or animal's body. The material may further exhibit anincrease of implant volume up to 200% after 24 month from theimplantation in the target structure. Such a material may further beeasily to be sterilized by γ-radiation. A suitable energy dose may bebetween 20 kGy and 30 kGy, in particular below 25 kGy.

A further aspect of the present invention is directed to a fixationdevice which is adapted for fixing an implantation pin according to theabove first aspect. The fixation device comprises an ultrasonicsonotrode comprising a vibration shaft adapted to generate ultrasonicvibrations at a tip provided on the vibration shaft. Furthermore, thefixation device comprises a guiding mechanism adapted to cooperate withthe implantation pin in order to align the guiding mechanism withrespect to the implantation pin and adapted to guide the vibration shaftand/or the tip provided at the shaft.

It may be seen that this aspect of the invention is to provide afixation device which, on the one hand, includes an ultrasonic vibrationsource and which, on the other hand, is adapted to apply the generatedultrasonic vibrations in a predetermined way to the above describedimplantation pin according to the first aspect of the invention in orderto liquefy the moldable material of the implantation pin in the regionof the moldable portion(s). In order to be able to apply the ultrasonicvibrations in such predetermined manner, the sonotrode comprises a tipat which ultrasonic vibrations are generated. Furthermore, a guidingmechanism is provided such that the position and moving direction of thevibrated tip can be controlled as desired during an operation.Specifically, the guiding mechanism may be adapted such that it maycooperate with structures of the implantation pin such as for examplethe surface or the circumference of the pinhead in order to align theposition of the fixation device with respect to the implantation pin.For this purpose, the guiding mechanism may have specially adaptedabutment surfaces in order to hold or fix the guiding mechanism to theimplantation pin.

Furthermore, the guiding mechanism may be adapted to guide the vibrationshaft and/or the tip relative to the implantation pin. For example, theguiding mechanism may have a sliding mechanism such that, after beingfixed relative to the implantation pin, the tip of the ultrasonicsonotrode can be slid or moved in a predetermined direction with respectto the guiding mechanism. In this way, the vibrating tip may be movedfurther into the molding portion of the implantation pin whileliquefying the moldable material therein and thereby pushing theliquefied moldable material through the channel of the implantation pin.

The ultrasonic sonotrode may be adapted to generate ultrasonicvibrations at the tip with a frequency of between 10 and 50 kHz,preferably between 20 and 30 kHz, and a suitable vibration amplitude maybe in the range between 1 and 100 μm, preferably between 5 and 30 μm.The vibrations can be generated preferably in a direction along thevibration shaft and/or in a direction perpendicular to the vibrationshaft. The entire construction of the sonotrode including the shaft andthe tip should be adapted such that the ultrasonic vibrations can besuitably transmitted via the vibration tip to a target region in animplantation pin. For example, the shaft and the tip should comprisesufficient rigidity in order to transmit the vibration energy via thevibration tip.

The guiding mechanism may be suitably adapted to hold or guide thesonotrode and/or its vibrating tip with respect to the implantation pinto which the guiding mechanism is fixed. Furthermore, a damping elementmay be provided on the guiding mechanism such that vibrations from thesonotrode are not substantially transmitted to the guiding mechanism inorder to avoid that the implantation pin is vibrated through the guidingmechanism at undesired locations.

According to a further embodiment, the guiding mechanism is adapted toguide the vibration shaft in a direction parallel along the longitudinalaxis of the implantation pin. In other words, the vibrating tip arrangedat the vibration shaft can be advanced in a direction parallel to thelongitudinal axis of the implantation pin guided by the guidingmechanism which itself may be fixed in relation to the implantation pin.In this way, the fixation device may be used for liquefying the moldablematerial of the implantation pin in predetermined regions, namely e.g.regions along the longitudinal middle axis of the implantation pin. Asthe channel of the implantation pin preferably also extends along thismiddle axis, the vibrating tip which preferably has a larger lateraldimension than the channel of the implantation pin, may be pushed intothe moulding portion of the implantation pin while liquefying themoldable material therein and thereby pushing the liquefied moldablematerial through the channel.

According to a further embodiment the tip on the vibration shaft has asmaller lateral dimension perpendicular to the longitudinal axis of theshaft than the pinhead of the implantation pin. In other words, thewidth of the tip is smaller than the width of the pinhead or, again inother words, the contact surface between the vibrating tip and thepinhead is smaller than the entire surface of the pinhead. Accordingly,when the vibrating tip is in contact with the pinhead of theimplantation pin, only a partial region of the pinhead which maycorrespond to the pinhead molding portion may be liquefied.Particularly, the geometry and/or cross-section of the vibrating tip maybe adapted to correspond to the geometry and/or cross-section of amolding portion of a given implantation pin.

According to a further embodiment the tip on the vibration shaft has asmaller lateral dimension perpendicular to the longitudinal axis of thevibration shaft than the shaft of the implantation pin. In other words,the width or the cross-section of the vibrating tip may be smaller thanthe width or the cross-section of the shaft of the implantation pin.Accordingly, the vibrating tip can be pushed for example into the shaftmolding portion of the shaft of the implantation pin in order to liquefythe moldable material in this part of the pin's shaft.

According to a further embodiment the tip on the vibration shaft mayhave regions of different lateral dimensions. In other words, the widthor the size of the cross-section of a tip may vary along the directionof the longitudinal axis of the vibration shaft. Accordingly, whileliquefying the moldable material and pushing the vibrating tip into theimplantation pin regions of different cross-section can be liquefied.For example, a distal portion of the vibrating tip may have a smallerwidth than the shaft of the implantation pin whereas a proximal portionis wider than the distal portion and has a width being slightly smallerthan the width of the pinhead of the implantation pin but possibly widerthan the shaft of the implantation pin.

According to a further aspect of the invention an implantation kit isprovided including an implantation pin according to the first aspect ofthe invention. Furthermore, the implantation kit may comprise a fixationdevice according to the second aspect of the invention. Additionally,the implantation kit may comprise further elements or components such asfor example a multitude of implantation pins of different geometry suchthat a surgeon can choose an implantation pin which matches the geometryof a recess previously prepared in a bone. Furthermore, a plurality ofvibrating tips for the sonotrode may be included in the implantation kitwherein the tips may have different geometries adapted to differentimplantation pins.

According to a further aspect of the present invention a method forimplanting an implantation pin according to the first aspect isprovided. The method comprises: inserting the implantation pin into atarget structure; applying ultrasonic vibrations to the pinhead moldingportion of the implantation pin thereby liquefying moldable material inthe pinhead molding portion; and forcing the liquefied moldable materialthrough the channel of the implantation pin.

For applying the ultrasonic vibrations and/or for pushing the liquefiedmoldable material into the channel a fixation device according to theabove described second aspect of the invention may be used.

According to an embodiment, the method further comprises preparing arecess in the target structure, e.g. a bone, such that the implantationpin can be inserted into the recess such that a main contact between theimplantation pin and the target structure appears between the pinhead ofthe implantation pin and a border region around the recess. In otherwords, the geometry of the recess and the geometry of the implantationpin to be fixed therein may be adapted such that the implantation pinfits into the recess such that a small gap between the implantation pinand the recess walls remains or such that there is only slight contactbetween the surface of the shaft of the implantation pin and the wallsof the recess. Then, the pinhead preferably having a larger width thanthe pin's shaft abuts to the surface of the target structure in theborder region around the recess thereby preventing further introducingthe implantation pin deeper into the recess. When ultrasonic vibrationsare applied to the implantation pin the occurring pressure is thenmainly transmitted to the surface of the target structure bordering therecess instead of being applied to a surface within the recess.

It has to be noted that embodiments of the invention have been describedwith reference to different subject matters. In particular, someembodiments have been described with reference to apparatus type claimswhereas other embodiments have been described with reference to methodtype claims. However, a person skilled in the art will gather from theabove and the following description that, unless otherwise notified, inaddition to any combination of features belonging to one type of subjectmatter also any combination between features relating to differentsubject matters, in particular between features of the apparatus typeclaims and features of the method type claims is considered to bedisclosed with this application.

The aspects and embodiments defined above and further aspects andembodiments of the present invention are apparent from the examples ofembodiments to be described hereinafter and are explained with referenceto the examples of embodiment. The invention will be described in moredetail hereinafter with reference to examples of embodiment but to whichthe invention is not limited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an implantation pin having an inside channel according toan embodiment of the present invention;

FIG. 2 shows an implantation pin having an additional channel at thepinhead according to a further embodiment of the present invention;

FIG. 3 illustrates an implantation method using an implantation pin anda fixation device according to an embodiment of the present invention;and,

FIG. 4 illustrates an implantation method using an implantation pin anda fixation device according to an alternative embodiment of the presentinvention;

It is to be noted that the figures are only schematic and not to scale.Corresponding reference signs have been used throughout the figures todesignate similar elements.

DETAILED DESCRIPTION

FIG. 1 shows an implantation pin 1 including a pinhead and a shaft 5.The entire implantation pin is made as an integral part from a moldablematerial being bio-compatible or bio-resorbable. The pinhead 3 comprisesa pinhead moulding portion 7. The shaft 5 comprises a shaft moldingportion 9. Both molding portions 7, 9 are arranged adjacent to a channel11 which connects the molding portions 7, 9 to discharge openings 13located at a distal extremity of the shaft 5. The channel 11 is arrangedlinearly along the longitudinal axis 15 of the implantation pin and twosub-channels 17 connect the channel 15 in the middle of the pin to thelateral surface of the shaft.

The width w₂ of the shaft 5 is smaller than the width w₃ of the pinhead.At the upper surface of the pinhead 3 a cylindrical recess 19 isprovided. The recess 19 has a smaller lateral dimension w₁ than thelateral dimension w₂ of the shaft 5.

The implantation pin 1′ in FIG. 2 further includes additional channels21 which lead to discharge openings 23 located at a lateral lowersurface portion of the pinhead 3′.

With respect to FIG. 3 an embodiment of a method for implanting andfixing an implantation pin according to an embodiment of the inventionis described.

First, a recess 31 is drilled into a target structure 33 such as a bone.Then, an implantation pin 1 as shown in FIG. 1 is inserted into therecess 31. Therein, an implantation pin 1 with such a geometry is chosensuch that the outline of the implantation pin 1 is slightly smaller thanthe recess 31 such that a small gap between the recess 31 and theimplantation pin 1 is established. The pinhead 3 of the implantation pin1 abuts to the upper surface 35 of the bone 33 in a contact region 37.

A fixation device 41 is set on top of the implantation pin 1. Thefixation device 41 comprises a sonotrode 43 with a vibration shaft 47and a tip 45 provided on the vibration shaft 47. The sonotrode 43includes an ultrasonic vibration generator to which the vibration shaft47 is fixed. The ultrasonic vibrations generated by an ultrasonicgenerator 49 are transmitted to the tip 45 via the vibration shaft 47.

In order to align the fixation device 41 with respect to the pin 1 aguiding mechanism 51 is provided. The lower portion of the guidingmechanism 51 is adapted to cooperate with the pinhead 3. In the upperportion of the guiding mechanism 51 there is a sliding mechanism 53which is adapted such that the shaft 47 of the sonotrode is linearlyguided when sliding along the sliding mechanism 53. Furthermore, therecess 19 in the pinhead 3 may help in aligning the tip 45.

The distal part of the vibrating tip 45 comprises a cylindrical endportion 61 having a concave surface 63 on its lower end.

When the tip 45 guided on the vibration shaft 47 is excited withultrasonic vibrations the mouldable material of the implantation pin 1liquefies in a contact region between tip's cylindrical end portion 61and pin 1. As the tip 61 is pushed towards the distal end of the pin 1the liquefied moldable material is forced through the channel 11 in thepin and exits through the discharge openings 13 into the gap between thepin 1 and the recess 31.

After resolidification of the moldable material the pin is reliablyfixed within the recess 31. During the fixation process, no excessiveforce has been applied to the inside of the recess 31 but the pressureapplied by the tip 45 of the sonotrode 41 is mainly transmitted to thecontact surface 37 and thereby applied to an outer surface 35 of thebone.

After the fixation device has been withdrawn from the pin 1 a spacerelement 71 is used to fill the remaining space within the pin 1 whichhas been generated when pushing the vibrating tip 61 through themoldable portions of the pin 1. Accordingly, the cross-section of thespacer 71 should substantially correspond to the cross-section of thevibrating tip 61. The spacer element 71 can be of any material as it isnot in direct contact with the vital tissue. For example, the spacerelement 71 can be provided with a metal such as to stabilize theimplantation pin itself consisting of a moldable plastics.

With respect to FIG. 4, an alternative embodiment of a method forimplantation and fixing an implantation pin 1′ as shown in FIG. 1 isdescribed.

The implantation pin 1′ further comprises channels 21 in the pinhead 3′.

The fixation device 41′ comprises a sonotrode 43′ with a vibration shaft47′ on which a vibrating tip 45′ is provided. The tip 45′ comprises alower portion 81 with a width smaller than the width of the shaft 5′ ofthe pin 1. When fixing the pin in the recess 31, first this lowerportion 81 of the tip 45′ is pushed into the implantation pin 1′ byliquefying the moldable material.

The tip 45′ further comprises an upper portion 83 having a width widerthan the lower portion 81. While pushing the vibrating tip 45′ into thepin and thereby pressing the moldable material through the channel 11′and into the gap between the pin 1′ and the recess 31, the upper portion83 will contact the upper surface of the pinhead 3′ after a certaindistance. The upper portion 83 of the tip 45′ will then liquefyadditional moldable material in the pinhead 3′ and this material willflow through the additional channels 21 and exit from the dischargeopening 23 lying above the surface of the bone. The liquefied moldablematerial will flow to the surface of the bone and “glue” the pinhead 3′to the bone in this region.

Again, after removing the fixation device from the fixed pin, a spacer71′ is introduced in the remaining hollow space within the pin 1′.

It should be noted that the terms “comprising” or “including” do notexclude other elements or steps and the “a” or “an” does not exclude aplurality. Also elements described in association with differentembodiments and aspects may be combined. It should also be noted thatreference signs in the claims shall not be construed as limiting thescope of the claims.

1-21. (canceled)
 22. A method for implanting an implantation pin, themethod comprising: providing an implantation pin made of a singlematerial which can be liquefied by applying energy in the form ofultrasonic vibrations, the pin having a head and a shaft with aninternal channel; inserting the implantation pin into a targetstructure; guiding a tip of an ultrasonic sonotrode vibrating shaft witha guide mechanism adapted to engage the implantation pin head; applyingthe ultrasonic sonotrode vibrating shaft to the implantation pin therebyliquefying the pin material, the vibrating shaft tip having a widthsmaller than a width of the implantation pin shaft and less than a widthof the channel in the shaft; and forcing the liquefied moldable materialthrough the channel of the implantation pin.
 23. The method according toclaim 22, further comprising: preparing a recess in the target structuresuch that the implantation pin can be inserted into the recess such thata main contact between the implantation pin and the target structureoccurs between the head of the implantation pin and a border regionaround the recess.
 24. A method for implanting an implantation pin in atarget structure comprising providing an implantation pin consistingentirely of a material which can be liquefied by applying ultrasonicvibrations, the implantation pin comprises a pinhead, a shaft comprisinga discharge opening wherein a channel extends internally along andthrough the pinhead and the shaft, the channel connecting the pinheadmolding portion to the shaft discharge opening, wherein material of thepinhead molding portion when liquefied by applying ultrasonicvibrations, can be pressed through the channel and out of the dischargeopening; inserting the implantation pin into bone and applyingultrasonic vibrations with an ultrasonic sonotrode comprising avibration shaft adapted to generate ultrasonic vibrations at a tipprovided on the vibration shaft wherein the tip on the vibration shafthas a width being smaller than a width of the shaft of the implantationpin and being larger than a width of the channel within the shaft of theimplantation pin; and guiding the vibrating tip of the ultrasonicsonotrode with a guiding mechanism adapted to cooperate with theimplantation pin in order to align the guiding mechanism with respect tothe implantation pin.
 25. The method according to claim 24, wherein theguiding mechanism guides the vibration shaft in a direction parallelalong the longitudinal axis of the implantation pin.
 26. The methodaccording to claim 24 wherein the tip on the vibration shaft has smallerlateral dimension perpendicular to the longitudinal axis of the shaftthan the pinhead of the implantation pin.
 27. The method according toclaim 24 wherein the tip on the vibration shaft has smaller lateraldimension perpendicular to the longitudinal axis of the shaft than theshaft of the implantation pin.
 28. A method for implanting animplantation pin in a target structure; providing an implantation pincomprising a one-piece molded body having first and second ends spacedalong an axis, the body having a head portion at the first end and ashaft portion extending from the head portion to the second end of thebody, the head portion having an outer surface having a larger dimensionin a direction transverse to the axis than the shaft portion, the bodycomprises a solid material which can be liquefied by the application ofultrasonic energy, the body having an internal axially extending channeltherethrough extending from the first to adjacent the second end, thechannel having an enlarged area with a larger transverse dimension inthe head portion, the enlarged area open to the first end of the body,the enlarged area capable of receiving a tip of a vibrating toolinserted therein through the open first end of the body and the channelin the shaft portion having first and second discharge channelsextending radially outwardly from the axially extending channel to anouter surface of the shaft portion adjacent the body second end and theaxially extending channel in the head portion having third and fourthdischarge channels extending radially outwardly from the axiallyextending channel to the outer surface of the head portion, the thirdand fourth discharge channels located above an outer surface of thetarget structure when the head portion contacts the outer surface of thetarget structure, inserting the implantation pin into the targetstructure; applying ultrasonic vibration to the pin thereby liquefyingthe solid material; and forcing the liquefied material through thechannel of the implantation pin and out the discharge channels.
 29. Themethod as set forth in claim 28 wherein the first and second dischargechannels extend on opposite sides of the shaft.
 30. The method accordingto claim 29 wherein the radially extending discharge channels extend atan angle towards the second end of the shaft.
 31. The method accordingto claim 28 wherein the molded body comprises a bioabsorbable polymerthat can be liquefied by application of energy in the form of ultrasonicvibrations.
 32. The method as set forth in claim 24 wherein the tip ofthe ultrasonic sonotrode comprises a cylindrical end portion having aconcave surface on its distal region.
 33. The method as set forth inclaim 22 wherein the first and second discharge channels extend onopposite sides of the shaft.
 34. The method according to claim 33wherein the radially extending discharge channels extend at an angletowards the second end of the shaft.
 35. The method as set forth inclaim 22 wherein the tip of the ultrasonic sonotrode comprises acylindrical end portion having a concave surface on its distal region.